This invention relates generally to a method for exchanging data, and more specifically to a method for exchanging data between a mobile asset, such as a train, and a fixed data center utilizing a wireless communication link.
The transmission of data over a radio frequency channel is well known in the art. There are several wireless communications systems that are commercially available, including both cellular and satellite based systems. It is also known that the effectiveness of the transmission of data over such systems is dependent upon an appropriately high signal to noise ratio during the data transmission. While the transmission of voice information may be accomplished in the presence of noise in the communication link, the transmission of data will require a much cleaner signal in order to avoid the corruption of the data. Corrupted data may be retransmitted, thereby increasing the time and cost involved with the data transfer. When utilizing such systems on a mobile asset, such as a truck, an automobile or a train, it is difficult to assure that a sufficiently high signal to noise ratio will be maintained throughout the entire duration of the data transmittal because changes of asset position relative to terrain and man-made obstacles will affect the radio frequency propagation channel characteristics.
Improved communications systems have been developed to address the need for reliable data transmission over a wireless network. For example, U.S. Pat. No. 5,826,198 issued on Oct. 20, 1998, to Bergins, et al., teaches an improved cellular telephone network containing a means for measuring the quality of the communications channel for insuring that data transmission is attempted only when the channel signal level is greater than a pre-defined value. Such systems increase the cost of the communication link, and they may function to inhibit communications without regard for other variables affecting the need for the data transmittal.